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Relativistic mean field calculations of multi-$bar{K}$ hypernuclei are performed by adding $K^-$ mesons to particle-stable configurations of nucleons, $Lambda$ and $Xi$ hyperons. For a given hypernuclear core, the calculated $bar{K}$ separation energy $B_{bar{K}}$ saturates with the number of $bar{K}$ mesons for more than roughly 10 mesons, with $B_{bar{K}}$ bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the $bar{K}$-meson densities peak, similarly to what was found for multi-$bar{K}$ nuclei. The calculations demonstrate that particle-stable multistrange ${N,Lambda,Xi }$ configurations are stable against strong-interaction
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We report on self-consistent calculations of single-K^- nuclear states and multi-Kbar nuclear states in 12C, 16O, 40Ca and 208Pb within the relativistic mean-field (RMF) approach. Gradient terms motivated by the p-wave resonance Sigma(1385) are found to play a secondary role for single-K^- nuclear systems where the mean-field concept is acceptable. Significant contributions from the Kbar N -> pi Lambda conversion mode, and from the nonmesonic Kbar NN -> YN conversion modes which are assumed to follow a rho^2 density dependence, are evaluated for the deep binding-energy range of over 100 MeV where the decay channel Kbar N -> pi Sigma is closed. Altogether we obtain K^- total decay widths of 50-100 MeV for binding energies exceeding 100 MeV in single-K^- nuclei. Multi-Kbar nuclear calculations indicate that the binding energy per Kbar meson saturates upon increasing the number of Kbar mesons embedded in the nuclear medium. The nuclear and Kbar densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor.
We evaluate the $sigma$ exchange contribution to the $bar{K}Ntobar{K}N$ scattering within a chiral unitary approach. We show that the chiral transition potentials for $pi pi to K bar{K}$ in the $t$-channel lead to a $sigma$ contribution that vanishes in the $bar{K}$ forward direction and, hence, would produce a null $sigma$ exchange contribution to the $K^-$ optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading order chiral Lagrangian gives an I=0 $pipito Kbar{K}$ amplitude proportional to the squared momentum transfer, $q^2$. This finding poses questions on the meaning or the origin of $sigma$ exchange potentials used in relativistic mean field approaches to the $K^-$ nuclear selfenergy. This elementary $sigma$ exchange potential in $bar{K}Ntobar{K}N$ is compared to the Weinberg-Tomozawa term and is found to be smaller than present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.
The real and imaginary parts of the bar K^0 d scattering length are extracted from the bar K^0 d mass spectrum obtained from the reaction pp to d bar K^0 K^+ measured recently at the Cooler Synchrotron COSY at Julich. We extract a new limit on the K^- d scattering length, namely Im a le 1.3 fm and |Re a| le 1.3 fm. The limit for the imaginary part of the K^- d scattering length is supported by data on the total K^- d cross sections.
We study the production of $Xi^-$-hypernuclei, $^{12}_{Xi^{-}}$Be and $^{28}_{Xi^{-}}$Mg, via the ($K^-,K^+$) reaction within a covariant effective Lagrangian model, employing the bound $Xi^-$ and proton spinors calculated by the latest quark-meson coupling model. The present treatment yields the $0^circ$ differential cross sections for the formation of simple s-state $Xi^-$ particle-hole states peak at a beam momentum around 1.0 GeV/c with a value in excess of 1 $mu$b.
The creation of a hypernucleus requires the injection of strangeness into the nucleus. This is possible in different ways, mainly using pi+ or K- beams on fixed targets. A review of hypernuclei production by K- at rest is here presented. When a K- stops inside a nucleus it can undergo the so called strangeness-exchange reaction, in which a neutron is replaced by a Lambda with the emission of a pion. By precisely studying the outgoing pions both the binding energy and the formation probability of the hypernuclei can be measured. New measurements from the FINUDA experiment on 7Li, 9Be, 13C and 16O, coupled with previous measurements on 12C and 16O, allowed for the first time the study of the formation of hypernuclei as a function of the atomic mass number A. The new measurements also offered the possibility of disentangling the effects due to atomic wave-function of the captured K- from those due to the pion optical nuclear potential and from those due to the specific hypernuclear states. These new results on the study of the hypernuclei production by K- at rest are here presented and discussed.
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